Microelectronic devices, such as semiconductor devices and field emission displays, are generally fabricated on and/or in microelectronic workpieces using several different types of machines (“tools”). In a typical fabrication process, several different processes are performed on a workpiece to form integrated circuits, micro-mechanical components and many other types of features. The operations involved in fabricating a semiconductor device, for example, include depositing materials, patterning, doping, implanting, chemical-mechanical polishing, electropolishing, heat treating, etching, etc. A conductive component, such as a contact or conductive line, is generally constructed by depositing one or more layers of conductive materials on the workpieces, and then etching and/or polishing (i.e., planarizing) the workpieces to remove a portion of the deposited material. As the size of the individual features on microelectronic devices decreases, there is a high demand for tools that can precisely deposit or polish materials.
Plating tools that plate metals or other materials on the workpieces are becoming an increasingly useful type of processing machine. Electroplating and electroless plating techniques can be used to deposit copper, solder, permalloy, gold, silver, platinum and other metals onto workpieces for forming blanket layers or patterned layers. A typical copper plating process involves depositing a copper seed layer onto the surface of the workpiece using chemical vapor deposition (CVD), physical vapor deposition (PVD), electroless plating processes, or other suitable methods. After forming the seed layer, a blanket layer or patterned layer of copper is plated onto the workpiece by applying an appropriate electrical potential between the seed layer and an anode in the presence of an electroprocessing solution. The workpiece is then cleaned, etched and/or annealed in subsequent procedures before transferring the workpiece to another processing machine.
FIG. 1A illustrates an embodiment of an electrochemical processing station 1 that includes a container 2 for receiving a flow of electroplating solution from a fluid inlet 3 at a lower portion of the container 2. The processing station 1 can include an anode 4, a diffuser 6 having a plurality of apertures 7, and a workpiece holder 9 for carrying a workpiece 5. The workpiece holder 9 can include a plurality of electrical contacts for providing electrical current to a seed layer on the surface of the workpiece 5. When the seed layer is biased with a negative potential relative to the anode 4 it is a cathode. In operation the electroplating fluid flows around the anode 4, through the apertures 7 in the diffuser 6 and against the plating surface of the workpiece 5. The electroplating solution is an electrolyte that conducts electrical current between the anode 4 and the cathodic seed layer on the surface of the workpiece 5. Therefore, ions in the electroplating solution plate the surface of the workpiece 5.
The electrochemical processing stations used in fabricating microelectronic devices must meet many specific performance criteria. For example, many processes must be able to form small contacts by filling vias that are less than 0.5 μm wide, and even less than 0.1 μm wide, with the plated layer of material. The layer of plated material should also be deposited to a desired, uniform thickness across the surface of the workpiece 5. One factor that influences the uniformity of the plated layer is the mass transfer of electroplating solution at the surface of the workpiece. This parameter is generally influenced by the velocity of the flow of the electroplating solution perpendicular to the surface of the workpiece and the motion of the workpiece. Another factor that influences the uniformity of the plated layer is the current density of the electrical field across the surface of the wafer.
One concern of existing electrochemical processing stations is providing a uniform mass transfer at the surface of the workpiece. Referring to FIG. 1A, existing processing stations generally use the diffuser 6 to enhance the uniformity of the fluid flow perpendicular to the face of the workpiece. Although the diffuser 6 improves the uniformity of the fluid flow, it produces a plurality of localized areas of increased flow velocity perpendicular to the surface of the workpiece 5 (indicated by arrows 8). The localized areas generally correspond to the position of the apertures 7 in the diffuser 6. The increased velocity of the fluid flow normal to the substrate in the localized areas increases the mass transfer of the electroplating solution in these areas. This typically results in faster plating rates in the localized areas over the apertures 7. Although many different configurations of apertures have been used in plate-type diffusers, these diffusers may not provide adequate uniformity for the precision required in many current applications.
Another concern of electrochemical processing stations is that the diffusion layer in the electroplating solution adjacent to the surface of the workpiece 5 can be disrupted by gas bubbles or particles. For example, bubbles can be introduced to the plating solution by the plumbing and pumping system of the processing equipment, or they can evolve from inert anodes. Consumable anodes are often used to prevent or reduce the evolvement of gas bubbles in the electroplating solution, but these anodes erode and they form a passivated film surface that must be maintained. Consumable anodes, moreover, often generate particles that can be carried in the plating solution. As a result, gas bubbles and/or particles can flow to the surface of the workpiece 5, which disrupts the uniformity and affects the quality of the plated layer.
Still another challenge of designing electrochemical processing stations for plating uniform layers is providing a desired electrical field at the surface of the workpiece 5. The distribution of electrical current in the plating solution is a function of the uniformity of the seed layer across the contact surface, the configuration/condition of the anode, and the configuration of the chamber. However, the current density profile on the plating surface can change. For example, the current density profile typically changes during a plating cycle because plating material covers the seed layer, or it changes over a longer period of time because the shape of consumable anodes changes as they erode and the concentration of constituents in the plating solution can change. Therefore, it can be difficult to maintain a desired current density at the surface of the workpiece 5.
Still another concern of electrochemical processing stations is that they are typically optimized for use with a single size of workpiece. The anode 4 and the diffuser 6 will accordingly have a size and shape that is specific to a particular size of workpiece. Using an anode 4 and a diffuser 6 designed for one size of workpiece to process a differently sized workpiece 5 will yield inconsistent and generally undesirable results. For example, a semiconductor wafer having a 150 mm diameter is small enough to fit in a processing station 1 designed for a 200 mm diameter wafer, but even if the workpiece holder 9 was modified to hold a 150 mm wafer, the flow patterns and electric field characteristics designed for a 200 mm wafer would yield an uneven plated layer on the smaller 150 mm wafer.
As a result, adapting a processing station 1 to handle a differently sized workpiece 5 typically requires substantial modification of the plating stations because it usually involves replacing at least the anode 4 and the diffuser 6. Replacing these parts, however, is frequently more difficult and time consuming than the simple schematic diagram of FIG. 1 would imply. This requires stocking separate supplies of differently-sized anodes and diffusers, and it also requires a significant amount of downtime to remove the anode/diffuser pair for one type of workpiece and then install an anode/diffuser pair for a different workpiece. If the anodes 4 are consumable, replacing them is complicated by the fact that they require maintenance of a passivated film layer for consistent operation. As a consequence, manufacturers typically optimize the processing station to process a single size workpiece and leave it unchanged. If the manufacturer wishes to produce two different sizes of workpieces, the manufacturer will commonly purchase an entirely separate processing machine so that each machine need only handle one size.
FIG. 1B illustrates an apparatus 10 for single-wafer processing in accordance with one embodiment of an LT-210C available from Semitool, Inc. of Kalispell, Mont. The apparatus 10 includes a housing 11 that encloses a plurality of processing chambers 20 and a workpiece loader 12 that receives containers 13 filled with microelectronic workpieces 5. The apparatus 10 also includes a transfer device 15 that removes the workpieces 14 from the containers 13, moves the workpieces 5 among the processing chambers 20, and returns the processed workpieces 5 to the containers 13. The transfer device 15, for example, can include a pair of robots 16 that move along opposite sides of a track 17. The robots 16 can move along the linear track independently from each other, and each robot can have an arm 18 and an end effector 19 carried by the arm. Existing linear track systems are shown in U.S. Pat. No. 5,571,325 issued to Ueyama, et al., PCT Publication No. WO 00/022808 and U.S. patent application Ser. Nos. 09/386,566; 09/386,590; 09/386,568; and 09/759,998, all of which are herein incorporated in their entirety by reference. Instead of the system shown in FIG. 1B, the transfer device can be a rotary system having one or more robots that rotate about a fixed location in the plating tool. One existing rotary transfer mechanism is shown in U.S. Pat. No. 6,136,163 issued to Cheung, et al. Many rotary and linear transfer mechanisms have a plurality of individual robots that can each independently access most, if not all, of the processing stations within an individual tool to increase the flexibility and throughput of the plating tool.
One concern of existing transfer mechanisms is that the wafers may collide with one another as the transfer mechanisms handle wafers within a tool. Because many processing apparatus have a plurality of individual robots that move independently from each other to access many processing chambers within a single apparatus, the motion of the individual robots must be orchestrated so that the workpieces do not collide with each other or components of the tool. This typically requires complex algorithms in the software for controlling the motion of the workpieces that define the “rules” of movement so that one robot does not conflict with another robot. The complexity of the software often necessitates significant processor capabilities and processing time, which accordingly increases the cost of the processing tools and reduces the throughput of workpieces. Additionally, errors in determining the position of the workpieces, executing the software, or calibrating the system can result in collisions between workpieces. Thus, it would be desirable to avoid collisions with workpieces in a manner that does not adversely impact other parameters of the processing apparatus.
Another concern of existing transfer mechanisms is that they typically have complex mechanical and electrical assemblies with several components. This increases the risk that a component may malfunction, causing downtime of the entire processing machine and/or collisions that damage the workpieces. Therefore, it would be desirable to reduce the complexity of the transfer mechanisms.
Yet another aspect of existing transfer mechanisms is that they may not provide sufficient freedom of motion of the workpieces. Although many robots have been developed that have six degrees of freedom, many of these robots are not used in processing apparatus for fabricating microelectronic workpieces because the additional degrees of freedom increase the complexity of the systems. As a result, many existing transfer mechanisms limit one or more motions of the robots, such as limiting the vertical motion of the robots. It will be appreciated that it would be desirable to maintain the freedom of motion for the robots while also reducing the probability of collisions between the workpieces and the complexity of the robots.
As shown in FIG. 1B, the apparatus 10 also includes a central power supply 30 that receives, for example, AC power and converts the AC power to other waveforms for use throughout the tool. For example, the output of the power supply 30 is provided to each of the electrodes in the plating chambers. Additional power supplies are generally used to operate solenoid valves 50 for directing fluid to and from the processing chambers 20, the workpiece loader 12 (to drive the motors and actuators that move and access the containers 13), and to two head controllers 40 (one of which is visible in FIG. 1B). The head controllers 40 are coupled to the processing chambers 20 to drive the motors that open, close, and otherwise operate the chambers 20.
The power provided from the power supply 30 to the electrodes in the processing chambers and the power provided from other power sources to other components of the tool are conducted along a power distribution network that typically comprises a variety of cable types that have different electrical characteristics (i.e., physical construction, impedance, electromagnetic coupling, noise immunity, etc.). Although variation in the electrical characteristics of the cables may be tolerable for the power conducted to the motors used in processing chambers, even subtle variations between the electrical characteristics of the power provided to the electrodes in electrochemical processing chambers can result in substantial differences and inconsistencies in the wafers.
One characteristic of some power distribution networks is that the power distribution lines used to provide power to electrodes in a first processing chamber may have different electrical characteristics than the power distribution lines that provide power to electrodes in a second electrochemical processing chamber. Further, the power distribution lines that provide power to the electrodes in the processing chambers may be electromagnetically coupled to other power distribution lines in the power distribution network. The signals transmitted to one processing chamber over one power line, for example, can be inductively and/or capacitively coupled with signals transmitted to other components. Many applications compensate for such inductive and/or capacitive coupling by shielding the power lines, but even shielding may not provide adequate protection in some instances. As a result, different processing chambers often effectively receive different chemical processing power signals.